This invention relates to the method by which a vacuum may be maintained between the interior of a storage tank and an interior flexible liner to prevent the collapse of the interior flexible liner as the fuel is removed from the storage tank.
The containment of liquids, slurries and other non-solid substances is currently provided by storage tanks. These storage tanks have been built of steel or similar metals in order to provide strength, but have also been built of durable plastics. Many of the storage tanks, particularly those for storing fuels, such as gasoline, heating oil and such, have been installed underground. Other storage tanks have been installed above ground or partially below the surface. Storage tanks are also used for the transport of fluids such as on railroad tank cars, trucks, watercraft and other transportation vehicles.
For a variety of reasons, it has been advantageous to install flexible liners internally within the storage tanks. These flexible liners provide a safety feature, preventing the escape of the stored fluid from the storage tank in the event that stresses, damage or corrosion cause a leak in the storage tank. Where the fuel contained is toxic or otherwise potentially harmful to the environment about the storage tank, the addition of an internal flexible liner has been an effective means of prevention of potential contamination. The presence of an internal flexible liner also serves to prevent the contamination of the stored fluid from external sources, such as ground water in underground tanks which might develop a crack or hole over time, or rainwater and other contaminants which might seep into above ground tanks if similarly damaged.
Many existing storage tanks, particularly underground fuel storage tanks, have been retrofitted with internal flexible liners to prevent ground contamination by potential leaks of the fuel. The flexible liner, whether installed in underground fuel storage tanks or other storage tanks, is typically maintained in place while the storage tank is empty, or only partially full, by means of negative pressure between the external wall of the flexible liner and the internal wall surface of the storage tank. Proper maintenance of the negative pressure or vacuum is not easy.
Therefore, it is a principal object of the invention to provide an improved method for establishing and maintaining the negative pressure or vacuum between the inner wall surface of the solid storage tank and the outer wall surface of the flexible liner, both during installation or replacement of the flexible liner and while the flexible liner is installed.